The present invention comprises a new and distinct cultivar of Hydrangea plant known by the varietal name ‘Horath’. The new variety was discovered in 2002 in a planned breeding program in Dresden, Germany. The purpose of the breeding program was to develop compact, blue Hydrangeas. The new variety is the result of a cross between breeding selection 30-89/3 (female parent, unpatented) and ‘Venice Raven’ (male parent, U.S. Plant Pat. No. 10,928, also referred to as Venedig). The vigor and growth habit of ‘Horath’ are similar to 30-89/3, but ‘Horath’ differs in flower color and foliage characteristics. The branching habit and inflorescence diameter of ‘Horath’ are similar to ‘Venice Raven’, but ‘Horath’ differs in color and growth habit. The new variety was first asexually reproduced in 2002 via propagation by cuttings in Germany. The new variety has been trial and field tested in Germany and has been found to retain its distinctive characteristics and remain true to type through successive propagations.
The following traits distinguish ‘Horath’ as a new and distinct cultivar from other Hydrangea varieties known to the breeder:                1. Stem quality;        2. Vigor;        3. Compact growth habit;        4. Forcing time; and        5. Color, after blue treatment.        
‘Horath’ is similar to another Hydrangea variety, ‘Atlantic Blue’ (unpatented), because they are both mopheads with good stem quality. However, ‘Horath’ differs from ‘Atlantic Blue’ in growth habit, inflorescence size and dark blue color after treatment.